Grumbles 69 thats correct. As you say, they often have no outward signs of their autism so it's perhaps a little unfair to blame the airline if you haven't told them.
I think the allocated seating idea is great and certainly will improve the product that is generally well liked by those who know. I'm all for it and hope that the trial will work. And it has to work for it to be rolled out fully.
However, some myths need to be put to bed. Firstly, comparatively very few flights have seating issues and the crew are generally fantastic at sorting this (I speak as a No.1 who rarely gets involved due to having to stay at doors 1) and the flight has to be almost jam packed 150+ (319) and 175+ (320). Even an overbooked flight usually leaves with a few spare seats. In fact, it's my belief that seat satisfaction is generally higher than allocated seating.
...But, the run up to the flight can be stressful. I think the "scrum" for most flights is a bit exaggerated. The main issue for me is the queuing for boarding, often before the inbound has arrived and for the bucket and spade routes there is generally the 'unknown' element that effects who perhaps don't fly very often.
Speedy Boarding. I've never been a huge fan of the product but 9/10 times it works. The 1/10 is generally the odd station that can't master the art of bussing the SB's. However, nearly all airports place SB's in a chained off area of the bus or at the front and are let off first using the appropriate door. Failing that they get their own bus. Some of the less resourced airports we fly to, such as PFO, manage to do that without issue. So bussing can and does work for speedy boarding.